Production method of multi-gauge strips

ABSTRACT

The present invention provides a method of producing a multi-gauge strip which has a thick portion and a thin portion which are continuously disposed along its length. The method of producing multi-gauge strips consisting of a relatively thick portion and a relatively thin portion formed along the widthwise direction while continuously transferring a strip material, is characterized by comprising the steps of: primarily forming a strip material by pressing the upper side thereof so as to make a groove in the lower side of the part where a thin portion is to be formed; and secondly forming the resulted strip by pressing the upper side of the primarily formed strip so as to form the part having a groove into a thin portion and the other part into a thick portion.

TECHNICAL FIELD

The present invention relates to a method for production of multi-gaugestrips (MGS) which are mainly used as materials for lead frames ofsemiconductors. Multi-gauge strips refer to a band-shaped memberconsisting of a thick portion and a thin portion which are continuouslydisposed along the lengthwise direction. The present invention relatesto a method of producing multi-gauge strips by using a general purposeroller or a press.

BACKGROUND ART

Multi-gauge strip is a member having a use in a lead frame whichsupplies electricity to semiconductor parts requiring great electriccapacitance or to electric or electronic parts, while supporting them.For example, it is used to supply electricity to heat generating parts,such as a power transistor or a connector, as well as to smoothlyradiate heat generated from such parts. Multi-gauge strip is generallyproduced by forming a thick portion and a thin portion in a strip madeof copper and a copper alloy, wherein the thin portion is used as a leadand the thick portion as a heat radiator.

Conventional multi-gauge strips are formed to have a thin portion ofwhich thickness is around 30% of that of a thick portion. However, itcannot be formed by a conventional rolling method, since such rollingwork makes the length of a thin portion more elongated. Therefore,various approaches which stretch a material to the widthwise directionhave been developed so as to form a thin portion.

In conventional methods for producing a multi-gauge strip, scalping of apart of a certain material so as to form a thin portion, or welding amaterial for a thin portion to each end of a thick portion or the likehave been used for a time. However, these methods are not currently usedowing to the poor competitiveness. In recent years, a mode of straininga material to the widthwise direction is mainly used.

Among the methods of producing multi-gauge strips, one of the mostcommonly used methods is a V-Mill-employing method as shown in FIG. 1.The method processes a strip material (2) which includes the formationof a groove (

) (1 b) in the upper side at the center of a dice (1), and then ofslopes (1 c) in each right and left side of the groove (1 b), whereinthe slopes (1 c) broadens from the acute angle part (1 a) so as to forma shape of V.

As approaching the strip material (2) to the dice (1), the centerportion of the strip material (2) inserted into the groove (1 b) isformed into a thick portion (2 a) shown in FIG. 2, and each side of thelower part of the thick portion (2 a) is cut by a right angled part (1d) and an acute angled part (1 a) in the upper part of the groove in thedice (1), forming a cut part (2 b) having a slanted surface (2 c) and alinear surface (2 d). When further advancing the strip material (2) atthis state, the dimension of the cut part (2 b) becomes increased owingto the gradually expanded slanted surface (1 c), and the cut part (2 b)is formed to a thin portion (2 e) by a flat part (1 e) of the dice (1).Then a multi-gauge strip (2) having the thick portion (2 a) and the thinportion (2 e) is formed. At this time, for forming the strip material(2) on the dice (1), a roll (not shown) moves in a back-and-forth motionin the feeding direction of a material or moves in a left-and-rightmotion at a right angle to the feeding direction of a material. Further,hammering of the upper side of the material at high speed is employed,or the dice (1) can be modified to have the shape of a roll for theformation.

DISCLOSURE OF INVENTION Technical Problem

However, in the above method, a roll should moves back-and-forth whileapplying pressure, and one of the reciprocal movement should be unloadedstate, therefore the production rate is low owing to the limitation inspeed and pressurization. Further, since the shape of a dice isstructured to comprise a V-shaped slope, the fabrication, maintenanceand repair thereof are difficult, and the shape of the acute angle partis weak against the applied pressure.

Particularly, for a W-shaped multi-gauge strip having two thickportions, the pressure should be increased as much as the volume of aprotrusion (2 f) in the groove, and this necessitate a high ejectingpower, thereby causing limitation in formation itself as well as amaterial transfer.

There is another method called MGR (Multi Grooved Roll), wherein a pairof the upper and the lower roll each of which has depression andprominence (3 a,3 b), respectively, and a pair of the upper and thelower roll having a flat surface (4 a,4 b) are placed alternately atmultiple stages in tandem, as shown in FIG. 3. In this method, the upperand the lower roll (3 a,3 b) pressurize both sides of a material (5) toform a bended part and a thin portion, then the upper and the lower rollhaving a flat surface (4 a,4 b) correct the depression and prominence ofthe formed material to a flat plane by repeated rolling. In other words,the thin portion is formed by being gradually widened in both left andright side directions.

In the method, when the width of a thin portion formed by a singlemovement of rolling is set to be wide, wave forms are produced in thethin portion, and when the width is set to be narrow, the number of apair of the upper and the lower roll having depression and prominencerespectively should be increased, increasing cost of tools in totalproduction cost. Therefore, through the correction using the upper andthe lower roll having a flat surface, the length of the thick portion isformed to be same with the length of the thin portion.

As another embodiment of aforementioned MGR method, multiple stages ofthe upper and the lower roll are placed in tandem for formation. Thismethod uses the upper roll (6) where a groove (6 a), flat surfaces (6 b)in each side of the groove, and a slope (6 c) are formed, and the lowerroll (not shown) having a flat surface with the upper roll, as shown inFIG. 4. The upper roll (6) forms a thick portion (7 a) by making thecenter portion of a material (7) be inserted into the groove (6 a), andat the same time the flat surfaces (6 b) and the slope (6 c) form a thinportion (7 b) and slopes (7 c) at both ends of the thin portion. Theabove procedure is repeated so as to gradually increase the width of thethin portion.

At this time, when the width of a thin portion is set to be wide inorder to reduce the number of rolls, the same result as obtained fromthe MGR method of FIG. 3 will be obtained. Therefore, it is made to havethe slopes formed in each end of the thin portion in widthwisedirection, and a correction procedure should be carried out by using theupper and the lower roll having a flat surface as in the above-describedMGR method of FIG. 3.

For the method shown in FIG. 3, the strip material forms into amulti-gauge strip, via the shape A, B and then C, as shown in thecross-sectional view of FIG. 5. In other words, by repeating theformation of the material from the sides to the center in the widthwisedirection, the width of the thin portion becomes increased whilereducing the width of the thick portion. Further, in the method shown inFIG. 4, the strip material is formed into a multi-gauge strip via theshape D, E and then F. In other words, formation is carried out in a waythat a thick portion is formed first at the center portion of thematerial and then the width of the thin portion is increased in eachside of the center portion of the material.

In the meantime, for the methods represented in FIGS. 4 to 6, a largenumber of rolls are required for the formation, which makes the cost oftools increased, and when a material passes through each formation roll,the speed would be limited because the position of a thick portion inthe widthwise direction should be maintained constantly. Further, sincedust is generated during the repeated pressurization of each side of thethick portion, defective rate is increased.

Moreover, in the above method, each roll arranged in tandem requires aspeed-increasing function, since the thicknesses of both of the thickportion and the thin portion are decreased as the material passesthrough each upper and lower roll, wherein the decrement contributes toan increase in length. Further, the material becomes hardened during therepeated formation procedure, thereby requiring large scale equipmentfor exclusive use.

Also, the methods described above have common problems that, whenforming the thin portion through repeated formation process of amaterial, the position of the material during formation is not fixed.Accordingly, the formation of a shape having a multiple number of thethick and the thin portions is structurally restricted.

Technical Solution

The present invention has been designed to dissolve the problems ofconventional arts. The object of the present invention is to provide amethod of producing multi-gauge strips in which the formation of a thickportion and a thin portion can be conducted simultaneously as theelongation rate in the lengthwise direction of the thick portion becomessynchronized with that of the thin portion, by firstly forming the thinportion having a groove in the lower side of the strip material, therebymaking a certain space between the groove and a lower roll, wherein thespace makes the elongation rate in the widthwise direction high when thethick portion and the thin portion in the upper side are formed.

For achieving the aforementioned object, the method of producingmulti-gauge st rips of the present invention characteristicallycomprises the following steps in a method of producing a multi-gaugestrip consisting of a relatively thick portion and a relatively thinportion formed along the widthwise direction while continuouslytransferring a strip material: primarily forming a strip material bypressing the upper side thereof so as to make a groove in the lower sideof the part where a thin portion is to be formed; and secondly formingthe resulted strip by pressing the upper side of the primarily formedstrip so as to form the part having a groove into a thin portion and theother part into a thick portion.

Further, according to the method of producing multi-gauge strips of thepresent invention, the groove formed in the primary forming step is inthe shape of a trapezoid or curved surface.

Still further, according to the method of producing multi-gauge stripsof the present invention, the primary forming step comprises formationof the strip material into a processed strip which has a thick portionformed at the center in the widthwise direction of the strip, and agroove (

) formed in each end of the lower side; and the second forming stepcomprises formation of the processed strip into a multi-gauge stripconsisting of a thick portion in the center and a thin portion at eachend of the thick portion.

Moreover, according to the method of producing multi-gauge strips of thepresent invention, the second forming step comprises formation of aW-shaped multi-gauge strip by forming a square-shaped depressed area atthe center in the upper part of the thick portion.

Further, according to the method of producing multi-gauge strips of thepresent invention, the primary forming step comprises formation of astrip material into a processed strip which has a multiple number ofgrooves in the lower side thereof and a thick portion between saidgrooves; and second forming step comprises formation of the processedstrip into a multi-gauge strip consisting of a multiple number of thickportions and thin portions therebetween, by forming the grooves in theinner part of the processed strip into a thin portion and then formingthe grooves at each end part simultaneously into a thin portion.

Still further, according to the method of producing multi-gauge stripsof the present invention, the formation of the grooves in the inner partinto a thin portion in the second forming step, is conductedsubsequently in order of grooves in the center and outward grooves.

Still further, according to the method of producing multi-gauge stripsof the present invention, the primary forming step comprises formationof a strip material into a processed strip having grooves formed in eachside of the protrusion at the center of the lower side, and a thickportion formed outside of the grooves; and a second forming stepcomprises formation of the processed strip into a multi-gauge stripconsisting of thick portions at each end thereof and a thin portionbetween the thick portions.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 and 2 are reference figures showing a method of producing amulti-gauge strip by using a conventional V-Mill.

FIGS. 3 to 6 are reference figures showing a method of producing amulti-gauge strip by using a conventional MGR method.

FIG. 7 is a conceptual plan view of the equipment for describing amethod of producing a multi-gauge strip according to the presentinvention.

FIG. 8 is a cross-sectional view showing a forming procedure accordingto a first embodiment of the present invention.

FIG. 9 is a cross-sectional view showing a forming procedure accordingto a second embodiment of the present invention.

FIG. 10 is a cross-sectional view showing a forming procedure accordingto a third embodiment of the present invention.

FIG. 11 is a cross-sectional view showing a forming procedure accordingto a fourth embodiment of the present invention.

NUMERALS USED IN THE MAJOR PART OF THE DRAWINGS

-   10: strip material-   20, 40, 45, 60: processed strip-   21, 41, 61: thick portion (of the processed strip)-   22, 42, 62: groove-   30, 50, 70: multi-gauge strip-   31, 51, 71: thick portion (of the multi-gauge strip)-   32, 52, 72: thin portion (of the multi-gauge strip)-   33: square-shaped depressed area (33)

MODE FOR THE INVENTION

Hereinafter, the method of producing multi-gauge strips according to thepresent invention is described by referring to the attached drawings asfollows:

According to the present invention, a method of producing multi-gaugestrips of the present invention comprises the following steps in amethod of producing a multi-gauge strip consisting of a relatively thickportion and a relatively thin portion formed along the widthwisedirection while continuously transferring a strip material: primarilyforming a strip material by pressing the upper side thereof so as tomake a groove in the lower side of the part where a thin portion is tobe formed; and secondly forming the resulted strip by pressing the upperside of the primarily formed strip so as to form the part having agroove into a thin portion and the other part into a thick portion.Specific examples according to the present method are described in thebelow.

EXAMPLE 1

The first embodiment of a method of producing a multi-gauge stripaccording to the present invention comprises the steps of: forming astrip material (10) into a processed strip (20) in which a thick portion(21) is formed at the center portion in the widthwise direction, andgrooves (

) (22) are formed in each end of the lower side; and forming theprocessed strip (20) into a multi-gauge strip (30) having thin portions(32) formed on each side of the thick portion (31) in the center, asshown in FIGS. 7 and 8.

At this time, the shape of the grooves (22) is not particularly limited,and may include curved groove such as circular or elliptical type, ortrapezoid.

The processed strip (20) is formed by a first lower roller (101) havingat least one protrusions (101) at each side end in the widthwisedirection, and a first upper roller having a flat surface (not shown),and the multi-gauge strip (30) is continuously formed by a second lowerroller (not shown) having a flat surface, and a second upper roller(102) having a groove (102) corresponding to the thick portion in thecenter.

The strip material (10) on the protrusion (101) of the first lower roll(101) is pressurized by the first upper roller. By the pressurization, agroove (22) having a shape of the corresponding to the protrusion isformed on the lower side of the strip, while forming a processed strip(20) which is elongated to the widthwise direction as well as thelengthwise direction. The groove (22) formed on the lower part of theprocessed strip (20) forms a space over the second lower roller having aflat surface. With respect to the space formed in the above, while theupper side of the processed strip (20) is being inserted into a groove(102) of the second upper roller (102) to form a thick portion (31), theflat portion of the second upper roller (102) makes the slanted area ofthe groove in the processed strip (20) gradually come into contact withthe upper side of the second lower roller, making the thickness of theslanted area of the groove reduced so that ends of the groove iselongated to the widthwise and the lengthwise direction, forming a thinportion (32). Accordingly, a multi-gauge strip (30) is finally, formedwhich consists of the thick portion (31) at the center and the thinportions (32) at each side of the thick portion.

The thickness of the thin portion in said processed strip (20) is formedto be larger than the required thickness of the thin portion of theresulting multi-gauge strip (30), since the upper side of the processedstrip (20) is to be stretched and elongated when contacting with thegroove (102) of the second upper roller (102). In other words, whileformation of the thick portion by the groove (102) of the second upperroller (102), the flat portion pressurizes the upper side of the groovepart of the processed strip (20) to stretch it in the widthwisedirection, thereby forming a thin portion. Simultaneously with that,nearly the same volume in each thick portion and thin portion iselongated in the lengthwise direction, too, thereby synchronizing theelongation rate in the lengthwise direction of the thick portion withthat of the thin portion. This is due to the cross-sectional shape ofthe processed strip (20) having a groove.

In the above, even if there is no extra volume to be elongated(stretched) in the thick portion and the thin portion, the formationprocess is carried out as same as above described, except foreliminating the rolling work for the corresponding volume reduction.Further, in the case that a multi-gauge strip should have a thin portionwith a large width, the slanted part of the groove in the processedstrip (20) which forms a space, is allowed to have an acute angle inorder to extend the length of the slanted part. In the case that amulti-gauge strip should have a thin portion with a relatively narrowwidth, the length of the slanted part of the groove is allowed to beshortened. Like these, the shape or dimension of the groove isoptionally adjusted depending on the standard required.

The formation process as described so far can be applied same to otherexamples, therefore further description on this is eliminated in otherexamples.

Instead of using rollers, a press and a cast, i.e. punch and die or thelike can be used for formation. The processed strip (20) is formed byusing a lower punch (110) having at least one protrusions (111) at eachend in the widthwise direction and a flat upper die (120). Themulti-gauge strip (30) is formed by using an upper punch (140) having agroove (141) corresponding to the thick portion (31) over the center ofa flat lower die (130).

EXAMPLE 2

This example 2 of the present invention demonstrates a method in which,when forming a processed strip (20) into a multi-gauge strip (30) in theabove example 1, a square-shaped depressed area (33) is formed on theupper side at the center of the thick portion (31), resulting inW-shaped multi-gauge strip (30), as shown in FIG. 9.

In this method, as an upper punch (240) for forming a W-shapedmulti-gauge strip (30), one having a groove (241) with the square-shapeddepressed area (242) formed in the center of the lower side is used. Inthis method, the pressure inside the groove (241) is increased as muchas the volume of the square-shaped depressed area (242) as compared tothe case in which a groove (241) is only formed in the upper punch(240), however the space formed in the lower side of the processed strip(20) increases the flexibility of the material. Hence, it does notnecessitate high pressure and it is possible to carry out formationwithout restriction on ejection and transfer of a material.

EXAMPLE 3

This example 3 of the present invention demonstrates a method whichcomprises: a step of forming a strip material into a processed strip(40) having a multiple number of grooves (42) in the lower side thereofand a thick portion (41) therebetween; and a step of forming theprocessed strip (40) into a multi-gauge strip (50) consisting of amultiple number of thick portions (51) and thin portions (52)therebetween, by forming the grooves in the inner part of the processedstrip (40) into a thin portion and then forming the grooves at each endsimultaneously into a thin portion, as shown in FIG. 10.

In this method, when forming the processed strip (40) into a multi-gaugestrip (50), it is preferred that the formation is conducted subsequentlyin order of grooves in the center of the processed strip (40) andoutward grooves, and then finally the grooves in the edge of theprocessed strip (40) is formed into a thin portion. In this case, thegroove can be formed as a trapezoid or curved groove.

Specifically, a strip material is formed into a first processed strip(40) having a multiple number of grooves in the lower side, by using alower punch (310) having a multiple number of protrusions and a flatupper die (320); then the first processed strip (40) is formed into asecond processed strip (45) in which the inner groove part is formedinto a thin portion, by using a flat lower die (330) and a first upperpunch (340) having protrusions corresponding to the inner grooves of thefirst processed strip (40); and finally the second processed strip (45)is formed into a multi-gauge strip (50) having a multiple number ofthick portions (51) and thin portions (52) formed therebetween by usinga flat lower die (330) and a second punch (350) having protrusions (351)corresponding to the grooves (42) of the first processed strip (40).

Instead of using a cast and a press of a punch and a die, rollers can beused for forming a multi-gauge strip (50).

EXAMPLE 4

This example 4 of the present invention demonstrates a method whichcomprises: a step of forming a strip material into a processed strip(60) having grooves (62) formed in each side of a protrusion (63) at thecenter of the lower side, and thick portions (61) which are formed oneach side of the grooves; and a step of forming the processed strip (60)into a multi-gauge strip (70) consisting of thick portions (71) at eachend and a thin portion (72) therebetween, as shown in FIG. 11.

In this method, the protrusion (63) of the processed strip (60) ispreferably formed to be a curved shape, and the grooves (62) cansuitably have either of a trapezoid or a curved shape.

Specifically, the strip material is formed into a processed strip (60)having a protrusion (63) at the center of the lower side of the strip,grooves (62) formed therebetween, and thick portions (61) formed on eachside of the grooves (62), by using a lower punch (410) having aprotrusion (411) where a groove (412) is formed in the center and a flatupper die (420); and then the processed strip (60) is formed into amulti-gauge strip (70) consisting of thick portions (71) at each endthereof and a thin portion (72) between the thick portions, by using aflat lower die (430) and an upper punch (440) having a protrusion (441)corresponding to the groove (62) of the processed strip (60).

In this method, since the inner protrusion (411) has a wire-like curvedshape, the elongation rate in the widthwise direction is higher thanthat in the lengthwise direction. In the other hand, in the slanted partof the groove, the elongation rate in the widthwise direction is higherthat that in the lengthwise direction, as aforementioned. Accordingly,it is possible to form rather wider thin portion in the center of themulti-gauge strip (70). Further, in this example also, rollers can beused, instead of using a die and a cast of a punch and a die.

In the above, the present invention has been described through thepreferred embodiments. However, the scope of the present invention isnot limited to such specific examples, and can be further modified by anordinarily skilled person in the art, without departing from the spiritof the present invention by referring to the claims attached hereto.

INDUSTRIAL APPLICABILITY

According to the method of producing multi-gauge strips of the presentinvention, it is possible to reduce investment cost by being capable offorming a multi-gauge strip with a general low-price equipment; todecrease production cost by using a reduced number of process toolsowing to the simplified forming process; to minimize the dustgeneration, thereby decreasing defective proportion while improvingproductivity at the same time; and to result in multi-gauge strips invarious shapes by allowing formation of a thick portion and a thinportion in optional location of a material. Therefore, the presentinvention may contribute to the development in industries related tosemiconductor parts and electric or electronic parts where suchmulti-gauge strips are used.

1. A method of producing multi-gauge strips consisting of a relativelythick portion and a relatively thin portion formed along the widthwisedirection while continuously transferring a strip material,characterized by comprising the steps of: primarily forming a stripmaterial by pressing the upper side thereof so as to make a groove inthe lower side of the part where a thin portion is to be formed; andsecondly forming the resulted strip by pressing the upper side of theprimarily formed strip so as to form the part having a groove into athin portion and the other part to a thick portion.
 2. The method ofproducing multi-gauge strips according to claim 1, wherein the grooveformed in the primary forming step is in the shape of a trapezoid orcurved surface.
 3. The method of producing multi-gauge strips accordingto claim 1, wherein the primary forming step comprises formation of thestrip material into a processed strip which has a thick portion formedat the center in the widthwise direction of the strip, and a grooveformed in each end of the lower side; and the second forming stepcomprises formation of the processed strip into a multi-gauge stripconsisting of a thick portion in the center and a thin portion at eachend of the thick portion.
 4. The method of producing multi-gauge stripsaccording to claim 3, wherein the second forming step comprisesformation of a W-shaped multi-gauge strip by forming a square-shapeddepressed area at the center in the upper part of the thick portion. 5.The method of producing multi-gauge strips according to claim 1, whereinthe primary forming step comprises formation of a strip material into aprocessed strip which has a multiple number of grooves in the lower sidethereof and a thick portion between said grooves; and second formingstep comprises formation of the processed strip into a multi-gauge stripconsisting of a multiple number of thick portions and thin portionstherebetween, by forming the grooves in the inner part of the processedstrip into a thin portion and then simultaneously forming the grooves ateach end part into a thin portion.
 6. The method of producingmulti-gauge strips according to claim 5, wherein the formation of thegrooves in the inner part into a thin portion in the second formingstep, is conducted subsequently in order of grooves in the center andoutward grooves.
 7. The method of producing multi-gauge strips accordingto claim 1, wherein the primary forming step comprises formation of astrip material into a processed strip having grooves formed in each sideof the protrusion at the center of the lower side, and a thick portionformed outside of the grooves; and a second forming step comprisesformation of the processed strip into a multi-gauge strip consisting ofthick portions at each end thereof and a thin portion between the thickportions.